The present invention relates generally to disc brake rotors as used in a vehicle braking system. More particularly, the invention relates to a vehicle brake rotor that incorporates a plurality of vanes designed to reduce noise generated in the brake system.
Noise generated during a brake application has been increasing as the size of vehicles has been decreasing. Attempts have been made to reduce the noise generated using various systems and methods. One such technique involves the use of sound adsorption coatings on the pad assembly. While such coatings have some effectiveness, the addition of the coating adds cost to the manufacture and at times, undesirable noise occurs when the thickness of the coating has not been uniform.
Another technique involves a disc brake pad assembly having clench tabs extending through rubber-like grommets in openings in a caliper housing leg so that the grommets are retained in the openings and the brake pad assembly is retained on the housing leg. The grommets provide a noise dampening action during braking to reduce noise.
Individual noise problems have been reduced through the modification of the ingredients in the composition of materials that make up a brake pad. In many of these cases, while noise may have been abated somewhat, the braking effectiveness of the system has been changed by the modification of the brake pad material, Still another technique of reducing brake noise involves affixing a ring damper about a periphery of a brake rotor in a disc brake system. The ring damper is held in place by a groove formed in the periphery of the disc and is pre-loaded against the rotor both radially and transversely.
The above techniques involve the reduction of noise by absorbing or masking the noise after it has been created or by adding costly complexity to the braking system. It would be advantageous to design the system to reduce the potential for the creation of noise. It has been suggested that much of brake squeal or noise is influenced by the excitation of the natural frequencies of a rotor caused by the rubbing of friction pads on a rotor surface. There is evidence that a disc brake rotor may have a dozen or more naturally occurring frequencies. While most of these are in the axial direction, others are in the torsional direction. In simulated braking applications only certain of these natural frequencies create brake noise or squeal. Every natural frequency of a vibrating system has associated with it a mode shape that describes the pattern of deformation associated with that natural frequency. In a continuous structure, the mode shape is generally accepted or described by defining the pattern of nodes (loci of points of zero deformation) on the surface of the structure. Experiments have shown that the mode shape of an annular circular plate, a shape like that of a brake rotor, includes nodal circles and diameters. Thus, a beneficial effect on brake noise should be attainable if the nodal diameter modes of an installed disc rotor are maintained at a maximum separation, thereby reducing or eliminating coupling of the nodal diameter modes in the audible frequency range.
A typical structure of a brake rotor includes a central disc portion that is adapted to be mounted to an axle of a vehicle as in known in the art, by fasteners. An extending portion typically connects one of a pair of rotor friction plates or cheeks to the central disc portion. An outboard plate is the portion of the rotor that includes a friction surface attached to the central disc portion adjacent to the wheel and faces outward from the vehicle body. An inboard plate faces inward toward the vehicle body.
A plurality of vanes extend from an inner surface of the first or outboard plate to connect a second inboard plate thereto. The vanes are typically arranged in a radial fashion about the rotor. The vanes hold the first and second plates in a parallel, side-by-side relationship. Typically, vanes have an overall regular elongate, rod, coffin or rectangular shape with a generally constant width and cross-sectional area. In other words, many current vanes start out a rectangular cross-section at one end and remain rectangular throughout the longitudinal distance of the vane at an opposite end. Similarly, a prior-art plate typically has a thickness or cross-section remaining substantially constant along the radial direction.
A rotor may possess a number of inherent resonance modes. In use, the rotor may generate vibrations including a mode characterized by radial (and potentially transverse and some tangential) displacement of the plates of the rotor. Further, the rotor may generate vibrations in a mode referred to as an X-mode, characterized by mainly transverse (with some radial and tangential) displacement of the plates of the rotor. A transverse modal vector is defined by one nodal diameters at the friction radius of the rotor and X order nodal diameters defined by the number of transverse antinodes. Coupling of a radial and an X-mode in a rotor results in a hybrid mode vibration. In a hybrid mode, one plate exhibits radial mode behavior and the other plate exhibits X-mode behavior.
It would be advantageous to provide an apparatus and method to prevent the occurrence of hybrid mode behavior in a disc brake rotor.
An aspect present invention provides a rotor for a disc brake including a pair of friction plates arranged coaxially in a parallel, spaced-apart relationship and a plurality of vanes extending between the pair of friction plates. The vanes have a proximal end, a distal end and a mid-portion extending between the proximal end and the distal end. The proximal end of a plurality of the plurality of vanes include a first width, the mid-portion including a second width, the first width being substantially greater than the second width.
Other aspects of the present invention provide a rotor wherein the first width of half the vanes is substantially greater than the second width. The first width of the other half of the vanes can be substantially the same as the second width. The first width of at least half the vanes can be from about 50 percent greater than the second width to about twice that of the second width.
In another aspect of the invention, a plurality of the plurality of vanes can include an inverted T-shaped portion adjacent the proximal end of the vanes. Half of the vanes can include an inverted T-shaped portion adjacent the proximal end of the vanes. The inverted T-shaped portion is at least 50% wider than a width of the mid-portion. The rotor may further include an angled portion located between each inverted T-shaped portion and the mid-portion.
An aspect of the present invention provide a method of reducing noise in a disc brake rotor including stiffening a radially inner portion of the brake rotor with a proximal portion of a plurality of vanes and reducing hybrid vibration modes in an audible frequency range. The proximal portion of the plurality of vanes can include an inverted T-shaped portion. Half of the plurality of vanes can include an inverted T-shaped portion at a proximal portion. The other half of the plurality of vanes can include a substantially constant width from a proximal portion to a distal portion of the vanes.
Another aspect of the present invention provides a rotor for a disc brake including means for stiffening a radially inner portion of the brake rotor with a proximal portion of a plurality of vanes and means for reducing hybrid vibration modes in an audible frequency range. The proximal portion of the plurality of vanes can include an inverted T-shaped portion. Half of the plurality of vanes can include an inverted T-shaped portion at a proximal portion. The other half of the plurality of vanes can include a substantially constant width from a proximal portion to a distal portion of the vanes.